A semiconductor dynamic quantity sensor of the above type has been proposed in which a substrate includes a semiconductor layer mounted on a support layer, and a weight portion displaceable in a predetermined direction, movable electrodes joined to the weight portion so as to be displaceable integrally with the weight portion, fixed electrodes disposed so as to confront the movable electrodes and elastically-deformable beam-shaped beam portions for displaying the weight portion are formed by forming trenches in the semiconductor layer.
FIG. 9 is a diagram showing a general planar construction of this type of semiconductor dynamic quantity sensor J100, and FIG. 10 is a cross-sectional view of the sensor J100 which is taken along a one-dotted chain line X—X of FIG. 9.
The semiconductor dynamic quantity sensor J100 as described above is formed by applying a well-known micromachining processing to a semiconductor substrate 10.
In this case, as shown in FIG. 9, the semiconductor substrate 10 constituting the semiconductor dynamic quantity sensor J100 is a rectangular SOI (silicon on insulator) substrate 10 having oxide film 13 as an insulating layer between a first silicon substrate 11 serving as a first semiconductor layer and also as a support layer and a second silicon substrate 12 serving as a semiconductor layer.
The semiconductor dynamic quantity sensor J100 is achieved by subjecting the second silicon substrate 12 of the semiconductor substrate 10 to trench etching to form trenches 14 so that a movable portion comprising beam portions 22, a weight portion 21 integrally formed with the beam portions 22 and movable electrodes 24, and fixed electrodes 31, 41 confronting the movable electrodes 24 are formed.
Each beam portion 21 has a spring function displaceable in a direction of arrow X of FIG. 9 in accordance with an applied dynamic quantity, and it has a beam-shape extending in the direction perpendicular to the displacement direction X. The weight portion 21 is supported by the beam portions 22 so as to constitute a spring-mass type mass portion which is supported by the beam portions 22 and uses the beam portions 22 as springs, and it is likewise displaceable in the displacement direction X.
The movable electrodes 24 are formed integrally with the weight portion 21, and are arranged in a comb-shape so as to project from both sides of the weight portion 21 in the direction perpendicular to the displacement direction X of the beam portions 22. The comb-shaped movable electrodes 24 are displaceable in the displacement direction X together with the beam portions 22.
The fixed electrodes 31, 41 are fixedly mounted on a first silicon substrate 11, and a plurality of fixed electrodes 31, 41 are arranged so as to be engaged with the gaps between the neighboring movable electrodes 24, and the side surfaces of the fixed electrodes 31, 41 are confronted to the side surfaces of the movable electrodes 24.
Here, in the semiconductor acceleration sensor J100 of FIG. 9, the total capacitance formed in the gaps between the movable electrodes 24 at the left side and the fixed electrodes 31 is represented by CS1, and the total capacitance formed in the gaps between the movable electrodes 24 at the right side and the fixed electrodes 41 is represented by CS2.
In the semiconductor dynamic quantity sensor J100, the distance between each movable electrode at the left side and each fixed electrode 31 and the distance between each movable electrode at the right side and each fixed electrode 41 are varied under application of a dynamic quantity, so that the capacitance CS1, CS2 between the electrodes 24 and 31 (41) is varied in connection with the above variation.
The signal corresponding to the capacitance difference (CS1−CS2) thus varied is output as an output signal from the semiconductor dynamic quantity sensor J100, and this signal is processed by a circuit portion (not shown) and finally output, whereby the dynamic quantity is detected.
The semiconductor dynamic quantity sensor J100 is manufactured as follows. That is, the trench etching is carried out from the surface of the second silicon substrate 12 serving as the semiconductor layer to form the movable portion including the weight portion 21 and the movable electrodes 24, the fixed electrodes 31, 41 and the beam portions 22 so that they are sectioned from one another, and then the weight portion 21 and the movable electrodes 24 and the insulating layer 13 below the beam portions 22 are removed by sacrifice layer etching to release these portions.
As described above, in the manufacturing process of the semiconductor dynamic quantity sensor J100, the gap of each beam portion 22 and the gap between each movable electrode 24 and each fixed electrodes 31, 41 are simultaneously formed by the trench etching.
In this case, various proposals have been made to improve the processing dispersion of the width of the beam portion 22, that is, the beam width and the interval between the movable electrode 24 and the fixed electrode 31, 41, that is, the electrode interval, which is caused by the trench etching (for example, see JP-A-2000-24965).
As described above, although various proposals have been made to improve the processing dispersion of the beam width and the electrode interval due to the trench etching, no improvement has been made to the processing dispersion of the thickness of the beam portion 22 and the thickness of the movable electrode 24.
In this type of semiconductor dynamic quantity sensor J100, the dynamic quantity is detected on the basis of the displacement using the spring-mass system of the beam portions 22, the weight portion 21 and the movable electrode 24, and the effect of the processing dispersion of the thickness of the beam portions 22 and the thickness of the movable electrode 24 on the sensor sensitivity cannot be neglected.
That is, such processing dispersion increases the sensitivity dispersion of the sensor, and it may adversely affect the yield and the precision of the sensor.